In digital video and/or graphics processing, noise may occur that may generate incorrect pixels. This noise may distort a video image and may interfere with viewing of the image content. Noise may also create issues with regard to processing of video data. In some cases, random noise may be introduced during transmission of the video data from one device to another. White noise may be generally characterized as a Gaussian distribution in spatial and/or temporal domains, other types of analog noises in the video signals may not be easily estimated. In various instances, noise may comprise an artifact of image processing, for example, an artifact of image compression. For example, MPEG compression may be lossy and, in some instances, it may distort the video content. In this regard, the more the video is compressed, that is, the higher the compression ratio, the less the reconstructed video resembles the original information. Some examples of MPEG video distortion are a loss of texture, detail, and/or edges. MPEG compression may also result in ringing on sharper edges and/or discontinuities on block edges. Because MPEG compression techniques are based on defining blocks of video image samples for processing, MPEG compression may also result in visible “macroblocking” that may result due to bit errors. In MPEG, a macroblock is the area covered by a 16×16 array of luma samples in a video image. Luma may refer to a component of the video image that represents brightness. Moreover, noise due to quantization operations, as well as aliasing and/or temporal effects may all result from the use of MPEG compression operations.
When MPEG video compression results in loss of detail in the video image it is said to “blur” the video image. When MPEG video compression results in added distortion on the video image it is said to produce “artifacts” on the video image. For example, the term “mosquito noise” may refer to MPEG artifacts that may be caused by the quantization of high spatial frequency components in the image. Mosquito noise may also be referred to as “ringing” or “Gibb's effect.”
Some of the characteristics of mosquito noise may comprise artifacts of 8×8 block Discrete Cosine Transform (DCT) operations in MPEG compression. While generally confined to a particular 8×8 block of video samples, in some instances, motion compensation may result in mosquito noise beyond the block boundary. Mosquito noise commonly appears near luma edges, making credits, text, and/or cartoons particularly susceptible to this form of artifact. Mosquito noise may be more common, and generally more severe, at low bit rates. For example, mosquito noise may be more severe when macroblocks are coded with a higher quantization scale and/or on a larger quantization matrix.
Mosquito noise may tend to appear as very high spatial frequencies within the processing block. In some instances, when the input video to the MPEG compression operation has any motion, the mosquito noise generated may tend to vary rapidly and/or randomly resulting in flickering noise. Flickering noise may be particularly objectionable to a viewer of the decompressed video image. In other instances, when the input video to the MPEG compression operation is constant, the mosquito noise that results is generally constant as well. Horizontal edges tend to generate horizontal ringing while vertical edges tend to generate vertical ringing. While mosquito noise may also occur in the color components or chroma of a video image, it may generally be less of a problem since it is less objectionable to a viewer of the decompressed video image.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.